The obesity pandemic is driving an unprecedented increase in the prevalence of type 2 diabetes. This proposal focuses on delineating the functions of the nuclear receptor PPAR in re-programming skeletal muscle fuel metabolism. PPAR, and the related nuclear receptor PPAR?, serve as key transcriptional regulators of lipid metabolism by binding conserved DNA response elements in target gene promoters. Although this classical PPAR-mediated mechanism suggests that these factors regulate shared targets, skeletal muscle-specific PPAR? and PPAR transgenic mice exhibit drastically distinct metabolic phenotypes. PPAR transgenics display many of the metabolic benefits of exercise in the absence of training, including increased muscle glucose uptake and utilization, improved exercise endurance, and an increase in slow-twitch muscle fibers. Conversely, PPAR? transgenic mice exhibit a metabolic phenotype similar to that of the obesity-related insulin resistant state, displaying myocyte triglyceride accumulation, high fatty acid oxidation rates, glucose intolerance and decreased exercise capacity. Transcriptional and metabolomic profiling results strongly suggest that while PPAR and PPAR? regulate many overlapping gene targets, a subset of genes is PPAR isotype-specific. Recently, we discovered a novel mechanism whereby PPAR regulates gene transcription in a manner distinct from PPAR?, through cooperation with AMP-activated protein kinase (AMPK) and transcription factor MEF2A. We hypothesize that PPAR, AMPK, and MEF2A form a complex that functions in activating transcription of target genes that play a role in re-programming skeletal muscle fuel metabolism. We will employ candidate and unbiased strategies, in PPAR transgenic mice and in primary muscle cells in culture, to further define the novel mechanisms (Aim 1) and downstream metabolic targets (Aim 2) involved in the PPAR-mediated regulation of skeletal muscle fuel burning capacity and substrate flexibility. In the long-term, we seek to use this information to identify novel therapeutic targets aimed at the prevention and treatment of obesity-associated diseases.